The Munich Security Conference opens on Friday with a speech by German Chancellor Friedrich Merz, one of 15 heads of state or government from European Union countries whom organisers expect to attend.
The many other expected guests at the conference that runs until Sunday include Ukrainian President Volodymyr Zelenskiy and Chinese Foreign Minister Wang Yi.
In keeping with the conference's tradition, there will also be a large delegation of members of the US Congress.
"Trans-Atlantic relations have been the backbone of this conference since it was founded in 1963 ... and trans-Atlantic relations are currently in a significant crisis of confidence and credibility," conference chairman Wolfgang Ischinger told reporters this week.
"So it is particularly welcome that the American side has such great interest in Munich."
At 2025's conference, held a few weeks into US President Donald Trump's second term, Vice-President JD Vance stunned European leaders by lecturing them about the state of democracy on the continent.
A series of Trump statements and moves targeting allies followed in the months after that - including, in January, his later-abandoned threat to impose new tariffs on several European countries in a bid to secure US control of Greenland, a semi-autonomous territory of NATO ally Denmark.
With Rubio heading the US delegation in 2026, European leaders can hope for a less contentious approach more focused on traditional global security concerns, though a philosophically similar one.
Rubio will face a heavy lift if he wants to calm the waters, however.
"In the end it's about trust: do we trust each other as partners and can this lack of trust be repaired?" said Claudia Major, a senior vice-president at the German Marshall Fund in Berlin.
"Particularly Greenland has been a fundamental change for Europeans. That one NATO ally threatens another NATO ally has deeply affected European trust in the trans-Atlantic relationship."
